It is well known in the art that metal tubes used in heat transfer devices are susceptible to wear, erosion and other degradations which may create weaknesses or other potential failure points. One typical prior art method to determine the cause of damage to a tube involves making a circumferential cut on the tube wall and removing the entire section of the tube having a damaged portion thereon. This method is useful where a straight length portion of the tube has been affected. However, access to more constricted areas and removal of relatively large sections of tubing is limited where the cutting procedure is performed from the interior of the tube. In particular, the aforementioned prior art method cannot be utilized where the damaged area is located in a bent section of the tube, such as a U-bend where stress cracking or corrosion is most likely to occur. In these latter cases it is desirable to remove only the damaged area by cutting away a small "coupon", plugging the tube and leaving the remaining section of tube in place. For purposes of this disclosure, the term "coupon" refers to a small specimen of a tube, which is typically circular, but may have any shape.
In addition, when a damaged area on a tube is identified before complete failure of the tube wall, it may be desirable to determine the cause thereof in an attempt to reduce the risk of further damage to the remaining tubes in the tube bundle and thereby extend the life of the tube bundle. Determination of the cause of damage requires laboratory examination of the affected area, which necessitates removal of at least a portion of the damaged area on the tube.